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Android APIs
public class

FileBackupHelper

extends Object
implements BackupHelper
java.lang.Object
   ↳ android.app.backup.FileBackupHelper

Class Overview

A helper class that can be used in conjunction with BackupAgentHelper to manage the backup of a set of files. Whenever backup is performed, all files changed since the last backup will be saved in their entirety. When backup first occurs, every file in the list provided to FileBackupHelper(Context, String...) will be backed up.

During restore, if the helper encounters data for a file that was not specified when the FileBackupHelper object was constructed, that data will be ignored.

Note: This should be used only with small configuration files, not large binary files.

Summary

Public Constructors
FileBackupHelper ( Context context, String... files)
Construct a helper to manage backup/restore of entire files within the application's data directory hierarchy.
Public Methods
void performBackup ( ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)
Based on oldState , determine which of the files from the application's data directory need to be backed up, write them to the data stream, and fill in newState with the state as it exists now.
void restoreEntity ( BackupDataInputStream data)
Restore one record [representing a single file] from the restore dataset.
void writeNewStateDescription ( ParcelFileDescriptor fd)
Called by BackupAgentHelper after a restore operation to write the backup state file corresponding to the data as processed by the helper.
Protected Methods
void finalize ()
Invoked when the garbage collector has detected that this instance is no longer reachable.
[Expand]
Inherited Methods
From class java.lang.Object
From interface android.app.backup.BackupHelper

Public Constructors

public FileBackupHelper ( Context context, String... files)

Added in API level 8

Construct a helper to manage backup/restore of entire files within the application's data directory hierarchy.

Parameters
context The backup agent's Context object
files A list of the files to be backed up or restored.

Public Methods

public void performBackup ( ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)

Added in API level 8

Based on oldState , determine which of the files from the application's data directory need to be backed up, write them to the data stream, and fill in newState with the state as it exists now. When oldState is null , all the files will be backed up.

This should only be called directly from within the BackupAgentHelper implementation. See onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor) for a description of parameter meanings.

Parameters
oldState An open, read-only ParcelFileDescriptor pointing to the last backup state provided by the application. May be null , in which case no prior state is being provided and the application should perform a full backup.
data An open, read/write BackupDataOutput pointing to the backup data destination. Typically the application will use backup helper classes to write to this file.
newState An open, read/write ParcelFileDescriptor pointing to an empty file. The application should record the final backup state here after writing the requested data to the data output stream.

public void restoreEntity ( BackupDataInputStream data)

Added in API level 8

Restore one record [representing a single file] from the restore dataset.

This should only be called directly from within the BackupAgentHelper implementation.

Parameters
data An open BackupDataInputStream from which the backup data can be read.

public void writeNewStateDescription ( ParcelFileDescriptor fd)

Added in API level 8

Called by BackupAgentHelper after a restore operation to write the backup state file corresponding to the data as processed by the helper. The data written here will be available to the helper during the next call to its performBackup() method.

This method will be called even if the handler's restoreEntity() method was never invoked during the restore operation.

Note: The helper should not close or seek the newState file descriptor.

Parameters
fd A ParcelFileDescriptor to which the new state will be written.

Protected Methods

protected void finalize ()

Added in API level 8

Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.

Note that objects that override finalize are significantly more expensive than objects that don't. Finalizers may be run a long time after the object is no longer reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup. Note also that finalizers are run on a single VM-wide finalizer thread, so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary for a class that has a native peer and needs to call a native method to destroy that peer. Even then, it's better to provide an explicit close method (and implement Closeable ), and insist that callers manually dispose of instances. This works well for something like files, but less well for something like a BigInteger where typical calling code would have to deal with lots of temporaries. Unfortunately, code that creates lots of temporaries is the worst kind of code from the point of view of the single finalizer thread.

If you must use finalizers, consider at least providing your own ReferenceQueue and having your own thread process that queue.

Unlike constructors, finalizers are not automatically chained. You are responsible for calling super.finalize() yourself.

Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.

Throws
Throwable